This invention is concerned with a device for the manufacture of self-sustaining cups of thin paper, suitable for containing foodstuffs and particularly cakes, pies, plumcakes and the like, during the steps of baking, automatic or manual manipulation, exposure and sale.
It is known to accommodate certain foodstuffs such as mentioned above in drawn metal baking-pans that, during the baking step, possibly with insertion of paper cups (xe2x80x9cpirottinixe2x80x9d or baking cups), in order to avoid direct contact with metal.
Such cups, comprising radially plaited paper sheets having a frustoconical shape, are not self-sustaining, so that, without an embanking structure, they tend to buckle, both because of the tendency of the raw batter to become flabby and because of the natural expansion of the batter itself during the baking stage.
To this purpose, containers of corrugated paper are sometimes used which comprise two parts, namely a bottom and a lateral band to make a wall. Aluminium containers are also used.
It is also known to support plaited-paper cups in seats made in cardboard trays, so that the cup is laterally contained with the seat profile, while being easily withdrawn after baking.
However, since the above products are to be distributed industrially, the practice has developed of using cups which, while having an adequate sturdiness, can nevertheless be easily and unexpensively manufactured. This condition is not satisfactorily met by the above-mentioned approaches.
Due to the above reasons, substantially frusto-conical cups have been made in different sizes, not only from aluminium sheet, but also from cardboard (sometimes coupled to other materials). U.S. Pat. No. 5,184,995 and U.S. Pat. No. 6,093,460, for instance, show how to mould cardboard cups having a curled lip to build a peripheral containing bead, which imparts the structure a good resistance to its coming apart. The bead is formed by a beading member or by a molding in the die, which bends the lip of the cup to make a curl.
However, the approaches of U.S. Pat. No. 5,184,995 and U.S. Pat. No. 6,093,460 are both suitable for handling cardboard of considerable thickness, say having a basic weight of 200 g/sq.m. or more, and therefore having a good inherent stiffness, and are not suitable, on the other hand, for the manufacture of thin-paper cups, i.e. made of paper of 50 g/sq.m. or less, corresponding to a thickness of a few hundredths of a millimeter. As a person skilled in the art will appreciate, the degree of dimensional accuracy required for the different parts of the die increases as the paper thickness is reduced: in fact, if the gap between the movable and the stationary portions of the die is smaller than the thickness of the paper, the latter is liable to be torn, while, on the other hand, if the gap is too large, the paper is liable to be creased and be wedged between the parts of the die, thus jamming it. It is difficult to achieve so small dimensional tolerances and even more difficult to maintain them during the operation of the die machine, particularly in consideration of the circumstance that the die is also subject to heating, on the one hand because of friction, on the other hand because of deliberate heating for the purpose of thermoforming the paper.
Furthermore, the peripheral bead made of a single curl, as provided for in U.S. Pat. No. 5,184,995 and U.S. Pat. No. 6,093,460 with reference to cardboard, is not sufficient in the case of thin paper, on the one hand because it is unpractivìcable to build the required curl in the paper, on the other hand because anyway the curl is not stiff enough to impart the desired solidity to the cup.
Finally, wear of the dies due to operation would cause a quick decay of the accuracy of the die in any case, and would force replacement after a very short life period.
A main object of the invention is therefore to provide a device for the inexpensive mass-production of self-sustaining thin paper cups.
Another purpose is to extend the useful life of the dies used for thermoforming the cups.
The above objects and advantages are achieved by the invention, together with other advantages which will appear below, by providing a device for manufacturing self-sustaining cups, having the features set out in claim 1. The dependent claims recite other advantageous features.